This invention relates to new and useful ultraviolet radiation sunscreen agents and compositions displaying enhanced protection and to methods of protecting human skin against the potentially harmful effects of sunlight.
Although a tan has long been considered a status symbol indicative of good health and the ability to secure sufficient leisure time to enjoy outdoor activities such as swimming, tennis, golf, skiing and the like, it has become very evident that excessive exposure of the human skin to sunlight is harmful.
It is well documented that human skin is sensitive to sunlight and artificial light containing radiation of wavelengths between about 290 nanometers (nm) and 400 nm. Ultraviolet radiation of wavelengths between about 290 nm and 320 nm (UV-B region) has been known to rapidly produce damaging effects on the skin including reddening or erythema, edema, blistering or other skin eruptions in more severe cases. Prolonged or chronic exposure to radiation in this wavelength range has been associated with serious skin conditions such as actinic keratoses and carcinomas. In recent years, concern has also been expressed regarding ultraviolet radiation of wavelengths above 320 nm (UV-A region) and the adverse effects of such radiation on human skin. The radiation between 320 and 400 nm also contributes to the premature aging of the skin. In addition, recent studies indicate that chronic sun exposure limits the immuno-response of the skin. There is also evidence that a tan will offer some protection against burning but is quite ineffectual against other types of solar damage.
Growing public awareness that the enjoyment of outdoor activities must go hand in hand with adequate sun protection has led to an unprecedented growth in the area of sunscreen products. A desirable sunscreen product should have the following attributes: protection in both the UV-A and UV-B ultraviolet radiation ranges; maintenance of coverage, i.e., waterproof and perspiration proof; application and use convenience, i.e., ease of application, invisibility, non-staining and non-greasy; and freedom from irritation as a result of its ingredients, in particular, its active sunscreen ingredients. Of recent interest in this area have been some concerns over the irritancy and sensitization problems that may occur in some individuals utilizing sunscreen products with high SPF values containing organic sunscreen agents.
The effectiveness of a sunscreen product is indicated by its sun protection factor (SPF). The sun protection factor is the ratio of the amount of exposure (dose) required to produce a minimal erythema reaction in protected skin to the amount required to produce the same reaction in unprotected skin. The absolute dose differs from person to person and is largely dependent on one""s genetic predisposition and ethnic origin. If a person would normally require ten minute exposure to sunlight to develop a minimal erythema reaction, this person when using an SPF 15 sunscreen product should be able to tolerate up to 150 minutes of sunlight without an erythema reaction. Recent public awareness of the problems of exposure to sunlight has led to a demand for sunscreen products with high SPF values, i.e., at or above SPF 8.
Ease of application and cosmetic appeal, on the other hand, are important in formulating sunscreen compositions. These characteristics rely on subjective evaluations such as visual and tactile impression by the user. Consumer research studies indicate that a sunscreen formulation should rub in easily, leave the skin non-sticky and, above all, should be invisible on the skin after application. Sunscreen compositions containing organic sunscreen agents have been found, in some cases, to be irritating to the skin. Therefore, use has been made of inorganic sunscreen agents, such as titanium dioxide and zinc oxide.
For example, Japanese Patent Application No. 1981-161,881, describes cosmetics containing 0.1-40% of ultrafine divided titanium oxide with a particle size of 10-30 nanometers (nm) which has been rendered hydrophobic. It indicates that when hydrophobically treated titanium oxide with a particle size of 10-30 nm is blended into cosmetic base materials, it transmits visible light but reflects and scatters the harmful ultraviolet rays. It has been found that when titanium dioxide of this particle size range is utilized as a sunscreen agent in sunscreen compositions, it may result in the loss of one of the most desired properties of such compositions, i.e., invisibility.
U.S. Pat. No. 5,028,417, issued Jul. 2, 1991, describes sunscreen compositions containing microfine titanium dioxide. The particle size of the titanium dioxide is required to be less than 10 nm. It also states that other sunscreen agents can be utilized with the titanium dioxide.
U.S. Pat. No. 5,340,567, issued Aug. 23, 1994 describes a sunscreen composition comprising a synergistic combination of titanium dioxide having a particle size of less than about 35 nm and zinc oxide having a particle size of less than about 50 nm with titanium dioxide and zinc oxide being present at given ratios.
German Patent No. 3,642,794 (1987) describes a cosmetic composition for preventing sunburn which contains 1-25% zinc oxide of a particle size of 70-300 microns. It further indicates that the composition may also contain titanium dioxide of a particle size of 30-70 microns. This composition is undesirable due to its unaesthetic whiteness characteristics at high SPF levels.
U.S. Pat. No. 5,188,831, issued Feb. 23, 1993, describes sunscreen compositions wherein the sunscreen effect is obtained from a blend of oil-dispersible ultrafine titanium dioxide and water-dispersible titanium dioxide. However, the SPF level obtained is only of 10 with a total concentration of titanium dioxide of 5.0% w/w.
World Patent Application WO 90/06103, published Jun. 14, 1990, describes titanium dioxide sunscreens where the microfine titanium dioxide particles are coated with a phospholipid, either through the use of a powder mill or through the making of a dispersion in an oil phase containing the phospholipid with a high shear mixer. The phospholipid coated titanium dioxide is then incorporated into sunscreen compositions. A high efficiency is claimed: the data presented shows SPF values of up to 11 for a 3.75% titanium dioxide concentration and up to 25 for a 7.5% concentration of titanium dioxide. The use of high shear mixer or a powder mill is a complicated and energy intensive process.
EP 535972 A1, published Apr. 7, 1993 describes a method of preparing sunscreens in which a dispersion of zinc oxide and/or titanium dioxide particles in an oil is formed by milling.
EP 619999 A2, published Oct. 19, 1994 describes an aqueous dispersion of particulate metallic oxide of particle size less than 200 nm mixed with an emulsifier and an oil phase and also an organic hydrophobic sunscreen to form an o/w emulsion. The resulting sun protection composition has a higher SPF than would be expected if there was only an additive effect. However, the titanium dioxide alone at 4% yielded a SPF of only 7 to about 11.
EP 628303, published Oct. 19, 1994 describes a process for preparing a sunscreen composition. It consists of mixing sunscreen particles of metallic oxide less than 200 nm dispersed in an oil with one or more emulsifier and/or organic sunscreens. The resulting sunscreen composition is claimed to have a SPF value considerably higher than expected. The high SPF is only obtained when a metallic oxide is blended with an organic sunscreen. In fact, when no organic sunscreen is used, the SPF value is only about 7.
WO 93/11742 describes sunscreen compositions comprising titanium dioxide and iron oxide of particle less than 200 nm preferably coated with a phospholipid.
An article published in DCI in September 1992 by Tioxide Specialties Ltd. describes various ways of incorporating oil or water dispersions of titanium dioxide in emulsions. However, no data is given on the resulting SPF values.
An article published in Cosmetics and Toiletries, Vol. 107, October 1992, describes various ways of formulating with a physical sunblock. The discussion focusses on using titanium dioxide in a dispersion or using an emulsifier which is also an effective dispersing agent for titanium dioxide. It states that SPF""s far above 20 can be achieved. However, no examples are given, nor does the article mention the specific sunscreen components or their compositions.
A brochure published by the Tioxide Company on Mar. 15, 1994, discloses organic sunscreens of high SPF values obtained without the addition of any organic sunscreens. When measured, the SPF of the sunscreen compositions was indeed that described. However, when the titanium dioxide concentration was measured, it was at least twice what was claimed.
It is, therefore, an object of the present invention to provide improved sunscreen agents and compositions.
It is another object of the present invention to provide sunscreen compositions containing sunscreen agents that overcome the disadvantages of heretofore available materials and provide adequate and safe protection for human skin.
It is a further object of this invention to provide methods of protecting human skin against the harmful effects of sunlight.
These and other objects and features of the present invention will become readily apparent to one skilled in the art from the detailed description given hereinafter.
The foregoing objects and other features and advantages of the present invention are achieved by sunscreen compositions containing inorganic sunscreen agents as the active ingredients. More particularly, the present invention relates to sunscreen compositions containing titanium dioxide and zinc oxide of preferred particle size ranges, of preferred coating and in preferred amounts and ratios as the sunscreen agents. These specific compositions permit the use of much lower amounts of the sunscreen active ingredients than previously achievable while still achieving the desired high SPF values for the compositions and without the unsightly whiteness which occurs in prior sunscreen compositions at concentrations above about 5%. In the sunscreen compositions of this invention, considerably higher concentrations of titanium dioxide may be used without incurring a whitening effect, e.g., even up to 15% with acceptable whiteness, or possible higher.
Furthermore, our invention does not rely upon the use of hydrophilic titanium dioxide preparations as required in the above noted patent, nor are energy intensive processes as powder milling, nor are organic sunscreen actives required for the high efficacy.
The compositions of this invention are oil-in-water emulsions containing at least the following components:
(a) an inorganic sunscreen agent, such as titanium dioxide or zinc oxide or a mixture thereof;
(b) an anionic emulsifier; and
(c) a carrier oil.
The compositions of this invention provide sunscreen formulations having and SPF of at least 10. They are easily made by simple mixing and provide an excellent dispersion of the inorganic sunscreen agent throughout the composition, thus ensuring even skin coverage. They are substantially invisible upon application to the skin.
The sunscreen compositions of this invention yield highly effective ultraviolet- (UV) blocking capabilities; that is, a given level of protection is provided with a significantly lower concentration of titanium dioxide than previously obtained using commercially available powdered titanium dioxides. They do not require the unusual processing methods previously necessary to disperse the titanium dioxide into an oil, such as preparation of sub-batch mill bases, high shear mixing or milling, or applying such milling procedures to the final product formulation. Typical titanium dioxide sunscreen compositions of SPF 15 require levels of titanium dioxide that impart a significant whitening effect to the skin; the compositions of this invention, minimize this disadvantage.
The composition invented is an oil-in-water emulsion that is cosmetically superior to conventional inorganic sunscreen preparations, including water-in-oil titanium dioxide-only formulations, at equivalent SPF ratings, due to the low levels of titanium dioxide needed in the invention system. The compositions of this invention can be used for sun protection in daily wear or facial products as well as recreational situations. Because of the efficiency of the system, the inventive formulations are significantly lower in cost than other sunscreen systems.
There are several ingredients that contribute to the unexpectedly high efficiency of the compositions"" blocking of UV radiation. These elements include the following materials:
The compositions of this invention should include one or more of a select group of anionic emulsifiers. In particular, certain salts of fatty acids are useful in the formulations of this invention. More particularly, the following anionic emulsifiers are useful in the compositions of this invention: sodium stearate, sodium laurate, sodium lauryl sulfate, DEA cetyl phosphate, dioctyl sulfosuccinate and the like. Most preferably, the emulsifier should be sodium stearate.
It is believed that straight-chain fatty acid salts, having relatively high melting points (about 70xc2x0 C. or higher), are preferred due to their structure. For example, branched fatty acid salts are not as acceptable for use in the compositions of this invention. The anionic emulsifiers should be present in the compositions of this invention in an amount from about 0.01 to about 10%, more preferably 0.1 to about 7% and most preferably from about 0.5 to about 5%. There may be additional emulsifiers present in the compositions of this invention, such as nonionic emulsifiers known to those of ordinary skill in the art, such as sorbitan esters and ethoxylated sorbitan esters, ethoxylated fatty acids, fatty alcohols and ethoxylated fatty alcohols, fatty glyceride esters and ethoxylated fatty glyceride esters and the like. However, there should be at least one anionic emulsifier present in order to achieve the products of this invention. The fatty acid salt emulsifiers may be added to the composition in the salt, or the salt may be formed in situ.
A carrier oil should also be present in the compositions of this invention. Preferably, such carrier oils should be selected from the group of polyether interrupted fatty acid esters.
More preferably, the carrier oil should be a C8 to C22 fatty alkyl(optionally polypropylenoxy)polyethylenoxy, ether carboxylate ester, the ester having an alkyl group which has from one to twenty-two carbon atoms, optionally straight or branched. Most preferably, the carrier oil should be a isopropyl propylene glycol-2-isodeceth-7 carboxylate, such as Velsan D8P3 or other commercially available materials sold by Sandoz under the Velsan trade name. Preferably, the carrier oil should be present in the composition in an amount of between about 0.1% and about 10%. More preferably, it should be present in the amount of between about 1% and about 5%. Most preferably, it should be present in the amount of between about 2% and about 3%.
Preferably, the oil phase should contain at least two materials, the polyether carrier oil and a conventional emollient known to those of ordinary skill in the art as useful in sunscreen products, such as mineral oil, ester oils or others known to those of ordinary skill in the art, such as mineral oils, vegetable oils, silicones, synthetic emollients such as fatty acid esters and the like. This emollient should be present in the formulation in a ratio to the carrier concentration of from about 1:1 to about 3:1, most preferably, about 2:1. The carrier oil and the emollient should compose from about 2% to about 20% of the composition by weight.
The third element which should be present in the compositions of this invention is an inorganic sunscreen compound, such as titanium dioxide, zinc oxide or combinations thereof. Preferably, titanium dioxide should be used having a particle size from of less than about 300 nm in diameter. It should be present in the composition in the amount of from about 2% to about 25%. More preferably, it should be present in the amount of from about 2% to about 15%. Most preferably, it should be present in the amount of from about 3% to about 10%. The inorganic sunscreen compound should be oil dispersible, and may be present with or without surface coating.
The ratio of titanium dioxide to the weight of the carrier oil and the emollient combined should be from about 0.3:1 to about 1:1. Most preferably, the ratio should be about 0.5:1 and 2:3. For example, a composition containing 15% titanium dioxide, 8.33% Velsan D8P3, 12.5% Miglyol and the remainder of the composition identical to that of Example 1 below, results in a sunscreen composition having an SPF of 63. The whiteness value of this composition is acceptable and is only slightly whitening on the skin.
The pH of the compositions of this invention should be maintained at a level above about 5, more preferably, above about 5.5. Maintaining the pH at this level will ensure that the anionic emulsifier remains in the salt form, which is important in retaining the stability of the product.
Additionally, the usual elements of a modern sunscreen emulsion system, such as a polymeric thickener/stabilizer, one or more additional emollient oil, microbial preservatives, antioxidants, fragrance, humectant, and of course the water vehicle are utilized without known selection or restraint.
The compositions of this invention can be in either liquid or aerosol form. They can be incorporated into various cosmetic and personal care products such as hand and body lotions, oils, ointments, lip balm products, facial cosmetics and the like.
The sunscreen compositions of this invention may be prepared using one of at least two methods: a two-vessel method, in whcih the oil and water phases are individually prepared, and a one- vessel method into which all ingredients are added in selected, specific order. Any of these processes will produce a smooth, uniform, white to light ivory emulsion.
In accordance with the two-vessel process, a water phase is prepared by measuring deionized water into a beaker and mixing. The elements of the water phase, including emulsifiers and humectants, chelators, thickeners, waterproofing agents, neutralizing agents and antioxidants should be added and the solution heated. The anionic emulsifier may be placed into the water phase or into the oil phase, depending upon the nature of the emulsifier. The oil phase is prepared separately in another vessel, including the anionic emulsifier, carrier oil and inorganic sunscreen agent. The two phases are then held at a relatively high temperature and mixed.
More specifically, in the two-vessel process, water phase is prepared by measuring deionized water into a beaker and mixing. Next, Carbopol 940 should be added and the composition mixed until properly hydrated. Propylene glycol and EDTA should then be added and the composition mixed until a homogeneous solution is achieved. The solution should then be heated to 70-80xc2x0 C. The solution should be maintained at 70-80xc2x0 C. for phasing.
The oil phase is then prepared by adding the following ingredients into a beaker: BHT, Velsan D8P3, Stearic Acid, Cetyl Alcohol and Miglyol 812. The beaker should be placed in a water bath on an electric hot plate. The ingredients should be heated to about 80xc2x0 C. or until melted. The titanium dioxide should be added slowly and the composition stirred at high speed until homogenous. The mixture should be maintained at about 80xc2x0 C. until phasing.
The composition may then be phased by adding the Oil Phase to the Aqueous Phase and mixing, holding the temperature at about 80xc2x0 C. for 5 minutes. Sodium hydroxide should then be added (as a 10% solution) and the composition mixed for 5 minutes at high speed. Next, the mixing speed should be reduced and cooling begun. When the temperature of the batch reaches 40-45xc2x0 C., Dowicil 200 solution may be added and, optionally, fragrance. The pH should be checked and adjust to 8.00-8.50 with a 10% solution of Sodium Hydroxide, if needed (target pH 8.25). Deionized water may be added as required to bring the batch to final weight. When the temperature of the batch reaches 28-32xc2x0 C., mixing and cooling may be discontinued.
In the one-vessel process, the water and oil phases may be made in the same vessel, provided that the components are added in an appropriate order. For example, the water phase should be created first, adding water and optionally certain emulsifiers which are compatible with the water phase to the vessel. The vessel should be heated to about 85xc2x0 to about 95xc2x0 C. Once the temperature reaches this level, the oil phase components may be added, including, optionally, the anionic emulsifier if it is oil-phase compatible and the carrier oil, as well as any additional oil-phase emulsifiers, antioxidants and emollients that may be desired. The temperature should be maintained at this level for about 15 minutes, and the inorganic sunscreen agent added slowly, and the composition mixed for a period of time of at least about 30 minutes. The pH may then be checked and adjusted to about 8.25, Dowicil, a preservative added as well as optional fragrance.
More specifically, deionized Water may be added to a beaker to which is slowly added Carbopol 940. Next, EDTA is added and the composition mixed at high speed for 15-20 minutes or until the Carbopol is properly hydrated. Heating of the mixture to 92-95xc2x0 C. should be begun and the required amount of Propylene Glycol added during this time. When the temperature reaches 92-95xc2x0 C., BHT, Velsan D8P3, Stearic Acid, Cetyl Alcohol and Miglyol 812 are added. The temperature of the mixture should be maintained at about 92-95xc2x0 C. for about 15 minutes. Then, titanium dioxide should be added and the composition mixed for 30 minutes. Sodium Hydroxide (as a 10% solution) should be added and the composition mixed for 30 minutes at 88-92xc2x0 C. The composition should be cooled and, at 40xc2x0 C., Dowicil 200 solution added as well as optional fragrance. The pH should be adjusted to about 8-8.5 with Sodium Hydroxide (target pH is 8.25). Finally, sufficient water should be added to bring the batch to the target weight.